The invention relates to a method for error detection and error correction, in particular in a diagnostic device in connection with a knock detection in an internal combustion engine, according to the preamble to the main claim.
It is known that in various devices, a diagnosis is carried out in which the components or signals supplied by components or sensors are tested for plausibility and in the course of such a plausibility test, a determination is made as to whether or not an error exists. When an error is detected, a substitute measure is activated or a substitute value is used in place of the measured value. An error that was detected once can also be recognized as corrected, i.e. the error was detected at an earlier point in time, but no is longer present. In this instance, the substitute measure is usually also deactivated.
In known diagnostic functions which are executed, for example, in the control unit of an internal combustion engine, values that are essential to regulating the engine are monitored for plausibility. For example, these values are signals supplied by sensors. An error is detected if the signal to be tested or a signal derived from it either exceeds or falls below a threshold. There is thus no error if the signal is within the permissible range. The threshold in this connection does not have to be fixed, but can be stored in a memory of the control unit as a characteristic field or a characteristic curve that depends on different operating points of the engine. In plausibility tests of this kind, it can be the case that an existing error is detected in one operating point, but not in another. This results in a detected error being recognized as corrected in the second operating point since is not present in this operating point. The substitute measure is then deactivated again although the error still exists in the first operating point. In addition, a plausibility test of this kind does not differentiate between error types.
A method for error detection and error correction which carries out a more extensive analysis has been disclosed by DE-P 197 560 81.4. In this known method for error detection and error correction, which relates to the monitoring of the functionality of a knock detection device in an internal combustion engine, the knock detection and the error correction are executed based on two different testing methods. In a first testing method, a so-called 0 test is executed in which no signal is sent to the evaluation circuit and in a second test, a test pulse is introduced. In both tests, the reaction of the system is evaluated. If one of the two diagnostic functions raises the suspicion of an error, a deviation from the usually alternating diagnosis is initiated and the diagnosis indicating the error is repeated. In the error correction, a similar procedure is executed and the method that led to the error correction is first repeated before a final error correction is recognized.
The method for error detection and error correction according to the invention has the advantage that a particularly reliable and dependable error detection is possible and also in particular, a reliable error correction is possible, in which incorrect recognitions of error correction are prevented. These advantages are achieved by the method for error detection and error correction according to the invention with the features of claim 1. To that end, the signal to be evaluated, a characteristic curve, or the error detection and error correction themselves are divided into different ranges and the error detection itself is permitted in each range; the error correction, however, is only registered if the error and the no longer existing error, i.e. the error correction, have occurred in the same range. Advantageously, the ranges are associated with different operating points. An error detection is then possible in each operating point. The error correction, however, is only permissible if the second operating point is disposed in the same operating range as the first operating point.
Other advantages of the invention are achieved by means of the measures disclosed in the dependent claims. In this connection, it is particularly advantageous to set up the operating ranges based on characteristic curves and/or characteristic fields. Characteristic curves or characteristic fields of this kind can, for example, be an error detection threshold which is given as a function of the operating point and the operating point, in turn, is a function of values of the internal combustion engine, for example the speed, the load, the temperature etc. If the sensor signal or a signal derived from it exceeds the error detection threshold, for example, then an error is detected
The possibility of differentiating between error types represents another particular advantage of the invention. Since an error correction is only registered if the error type and the operating point in which the error no longer occurs coincide with each other, a particularly reliable error correction is achieved in which incorrect error detections and incorrectly recognized error corrections are prevented to the greatest extent possible.